This invention is directed to novel vanilloid receptor VR1 ligands. More particularly, this invention relates to novel β-aminotetralin-derived ureas that are potent antagonists or agonists of VR1 and exhibit activity in animal models of hyperalgesia and colitis, and are useful for the treatment and prevention of pain conditions in humans including arthritis, and for the treatment of irritable-bowel syndrome and associated conditions.
Noxious chemical, thermal and mechanical stimuli excite peripheral nerve endings of small diameter sensory neurons (nociceptors) in sensory ganglia (e.g., dorsal root, nodose and trigeminal ganglia) and initiate signals that are perceived as pain. These neurons are crucial for the detection of harmful or potentially harmful stimuli (heat) and tissue damage (local tissue acidosis and/or stretch) that arise from changes in the extracellular space during inflammatory or ischaemic conditions (Wall, P. D., and Meizack, R., Textbook of Pain, 1994, New York: Churchill Livingstone). Nociceptors transduce noxious stimuli into membrane depolarization that triggers action potential, conducts the action potential from the sensory sites to the synapses in the CNS, and conversion of action potentials invokes a perception of pain, discomfort, and appropriate mechanical/physical protective reflexes. At the molecular level, nociception is carried out by ion channels or receptors. Plant derived vanilloid compounds (capsaicin and its ultrapotent analog, resiniferatoxin, etc.) are known to selectively depolarize nociceptors and elicit sensations of burning pain—the sensation that is typically obtained by hot chili peppers. Therefore, capsaicin mimics the action of physiological/endogenous stimuli that activates the “nociceptive pathway”. Recent advances in pain biology have identified receptors for vanilloids, protons (i.e., acidic solutions), and for heat. Because nociceptors are involved with unwanted pain and inflammatory conditions in human beings and animals, modulation of their nociceptive pathway is important in palliative and other therapies.
Walpole and colleagues at Sandoz reported on the first competitive antagonist of the sensory neuron excitants capsaicin and resineriferatoxin (Walpole, C. S. J. et. al., J. Med. Chem. 1994, 37, 1942). Subsequently, capsazepine has been shown to be a vanilloid receptor antagonist. Capsazepine, however, is not aminotetralin-derived. Jee Woo Lee and colleagues at Pacific Corporation disclosed thiocarbamic acid derived VR1 antagonists in WO0216317A1 and vanilloid receptor modulators in WO0216318A1 and WO0216319A1 but these applications do not disclose or describe α-substituted β-aminotetralins. Hutchinson and colleagues at Neurogen describe a diaryl piperazinyl ureas and related compounds as capsaicin receptor ligands in WO02082212A1 but aminotetralins are not covered. Scientists at the Universidad Miguel Hernandez in Alicante, the Universidad de Valencia and the Consejo Superior de Investigaciones Cientificas (CSIC) in Barcelona have used a combinatorial chemistry-based approach to discover compounds that modulate the vanilloid VR1 receptor and have disclosed two trialkylglycine-based compounds as noncompetitive VR1 channel blockers (Garcia-Martinez, C. et al. Proc Natl Acad Sci USA 2002, 99(4): 2374) but none are aminotetralin-derived.
U.S. Pat. Nos. 6,140,354 and 6,201,025 by Dax et. al. teach the synthesis of N-acylated and N-alkylated α-substituted β-aminotetralins but do not describe the synthesis of ureido β-aminotetralins. U.S. Pat. No. 6,169,116 B1 by Swoboda describes β-aminotetralins and their pharmaceutical uses but does not describe the synthesis of α-substituted β-aminotetralins and does not describe the synthesis of ureido β-aminotetralins. European patent application 0064964 by Arvidsson teaches the synthesis of N-alkylated α-alkyl-β-aminotetralins in which the alkyl substituent in the α-position is hydrogen or C1-6alkyl but does not describe the synthesis of β-aminotetralins substituted with groups other than hydrogen or C1-6alkyl in α-position nor describe the synthesis of ureido β-aminotetralins.
Thus, there is a need for potent modulators of VR, and in particular, for novel β-aminotetralin-derived ureas that exhibit potent binding affinity for the human and rat VR1 ion channel. There is also a need for novel β-amino-tetralin-derived ureas that act as potent functional antagonists and/or agonists of the human and rat VR1 ion channel. Finally, there is a need for novel β-aminotetralin-derived ureas that bind with high affinity to VR1 and also act as potent functional antagonists of the human and rat VR1 ion channel.